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String.Format Method (IFormatProvider, String, Object[])

Replaces the format item in a specified string with the string representation of a corresponding object in a specified array. A specified parameter supplies culture-specific formatting information.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static string Format(
	IFormatProvider provider,
	string format,
	params Object[] args
)

Parameters

provider
Type: System.IFormatProvider
An object that supplies culture-specific formatting information.
format
Type: System.String
A composite format string (see Remarks).
args
Type: System.Object[]
An object array that contains zero or more objects to format.

Return Value

Type: System.String
A copy of format in which the format items have been replaced by the string representation of the corresponding objects in args.

ExceptionCondition
ArgumentNullException

format or args is null.

FormatException

format is invalid.

-or-

The index of a format item is less than zero, or greater than or equal to the length of the args array.

This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its string representation and to embed that representation in a string. The .NET Framework provides extensive formatting support, which is described in greater detail in the following formatting topics:

The provider parameter supplies custom and culture-specific information used to moderate the formatting process. The provider parameter is an IFormatProvider implementation whose GetFormat method is called by the String.Format(IFormatProvider, String, Object[]) method. The method must return an object to supply formatting information that is of the same type as the formatType parameter. The provider parameter's GetFormat method is called one or more times, depending on the specific type of objects in args, as follows:

  • It is always passed a Type object that represents the ICustomFormatter type.

  • It is passed a Type object that represents the DateTimeFormatInfo type for each format item whose corresponding data type is a date and time value.

  • It is passed a Type object that represents the NumberFormatInfo type for each format item whose corresponding data type is numeric.

For more information, see the Format Providers section of the Formatting Types topic. The Example section provides an example of a custom format provider that outputs numeric values as customer account numbers with embedded hyphens.

The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items, that correspond to an object in the parameter list of this method. The formatting process replaces each format item with the string representation of the value of the corresponding object.

The syntax of a format item is as follows:

{index[,length][:formatString]}

Elements in square brackets are optional. The following table describes each element. For more information about the composite formatting feature, including the syntax of a format item, see Composite Formatting.

Element

Description

index

The zero-based position in the parameter list of the object to be formatted. If there is no parameter in the index position, a FormatException is thrown. If the object specified by index is null, the format item is replaced by String.Empty.

,length

The minimum number of characters in the string representation of the object to be formatted. If positive, the object to be formatted is right-aligned; if negative, it is left-aligned. The comma is required if length is specified.

:formatString

A standard or custom format string that is supported by the object to be formatted. Possible values for formatString are the same as the values supported by the object's ToString(format) method. If formatString is not specified and the object to be formatted implements the IFormattable interface, null is passed as the value of the format parameter that is used as the IFormattable.ToString format string.

NoteNote

For the standard and custom format strings used with date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings. For the standard and custom format strings used with numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the standard format strings used with enumerations, see Enumeration Format Strings.

The leading and trailing brace characters, "{" and "}", are required. To specify a single literal brace character in format, specify two leading or trailing brace characters; that is, "{{" or "}}".

If the string assigned to format is "Thank you for your donation of {0:####} cans of food to our charitable organization." and arg[0] is an integer with the value 10, the return value will be "Thank you for your donation of 10 cans of food to our charitable organization."

The following example uses the String.Format(IFormatProvider, String, Object[]) method to display the string representation of some date and time and numeric values using several different cultures.


using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      string[] cultureNames = { "en-US", "fr-FR", "de-DE", "es-ES" };

      DateTime dateToDisplay = new DateTime(2009, 9, 1, 18, 32, 0);
      double value = 9164.32;

      Console.WriteLine("Culture     Date                                Value\n");
      foreach (string cultureName in cultureNames)
      {
         CultureInfo culture = new CultureInfo(cultureName);
         string output = String.Format(culture, "{0,-11} {1,-35:D} {2:N}", 
                                       culture.Name, dateToDisplay, value);
         Console.WriteLine(output);
      }    
   }
}
// The example displays the following output:
//    Culture     Date                                Value
//    
//    en-US       Tuesday, September 01, 2009         9,164.32
//    fr-FR       mardi 1 septembre 2009              9 164,32
//    de-DE       Dienstag, 1. September 2009         9.164,32
//    es-ES       martes, 01 de septiembre de 2009    9.164,32


The following example defines a customer number format provider that formats an integer value as a customer account number in the form x-xxxxx-xx.


using System;

public class TestFormatter
{
   public static void Main()
   {
      int acctNumber = 79203159;
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:G}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:S}", acctNumber));
      Console.WriteLine(String.Format(new CustomerFormatter(), "{0:P}", acctNumber));
      try {
         Console.WriteLine(String.Format(new CustomerFormatter(), "{0:X}", acctNumber));
      }
      catch (FormatException e) {
         Console.WriteLine(e.Message);
      }
   }
}

public class CustomerFormatter : IFormatProvider, ICustomFormatter
{
   public object GetFormat(Type formatType) 
   {
      if (formatType == typeof(ICustomFormatter))        
         return this; 
      else
         return null;
   }

   public string Format(string format, 
	                     object arg, 
	                     IFormatProvider formatProvider) 
   {                       
      if (! this.Equals(formatProvider))
      {
         return null;
      }
      else
      {
         if (String.IsNullOrEmpty(format)) 
            format = "G";

         string customerString = arg.ToString();
         if (customerString.Length < 8)
            customerString = customerString.PadLeft(8, '0');

         format = format.ToUpper();
         switch (format)
         {
            case "G":
               return customerString.Substring(0, 1) + "-" +
                                     customerString.Substring(1, 5) + "-" +
                                     customerString.Substring(6);
            case "S":                          
               return customerString.Substring(0, 1) + "/" +
                                     customerString.Substring(1, 5) + "/" +
                                     customerString.Substring(6);
            case "P":                          
               return customerString.Substring(0, 1) + "." +
                                     customerString.Substring(1, 5) + "." +
                                     customerString.Substring(6);
            default:
               throw new FormatException( 
                         String.Format("The '{0}' format specifier is not supported.", format));
         }
      }   
   }
}
// The example displays the following output:
//       7-92031-59
//       7-92031-59
//       7/92031/59
//       7.92031.59
//       The 'X' format specifier is not supported.


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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